Final answer:
The number of vacancies in a body-centered cubic structure of iron at 850°C cannot be determined without additional data on the energy of vacancy formation or a specific formula. The structure consists of two atoms per unit cell.
Step-by-step explanation:
The question pertains to the determination of the number of vacancies per cubic meter in iron at a given high temperature. Specifically, at 850°C the number of vacancies in a body-centered cubic (bcc) structure of iron. The body-centered cubic structure consists essentially of one atom at the center of the cube and one-eighth of an atom at each of the eight corners, effectively totaling two atoms per unit cell.
To calculate the number of vacancies, typically, an equation involving the material's energy of vacancy formation, the Boltzmann's constant, and the temperature is used. However, the question doesn't provide sufficient information such as the energy of vacancy formation or a specific formula to use. In this case, without additional data or context, it's not possible to provide a definitive answer from the options given (A, B, C, D).